This invention relates to a tractor assembly, and more particularly to a unitary assembly of at least three tractors and an implement for moving earth or the like.
There is an increasing demand for moving large volumes of overburden such as in strip mining, and this need is currently being met with the largest forms of earthmoving equipment and with dual or tandem operated vehicles. For example, two crawler tractors have been coupled to each other in side-by-side relation for powering a single bulldozer blade. In such instance, the individual tractors are smaller than an equivalently powered single tractor, and they can be disengaged from each other and the implement for separate use, easier maintenance, and easier shipping purposes.
However, with a single bulldozer blade spanning between the front of two tractors, it is difficult to vary the position of the blade because of the length limitations of the extensible and retractable hydraulic jacks connected thereto, and to obtain the desired angularity of the blade relative to the normal forward direction of longitudinal movement. Specifically, it is difficult to angle the blade sufficiently to optimize side casting of the overburden. Moreover, when the blade is positioned for maximized side casting ability, the leading edge requires more tractive effort or drawbar pull of the tractor on that side.
Still another problem resides in the fact that when the aforementioned side casting side-by-side tractor assemblies reach the end of a long row they often must be operated in reverse back to the start of the row without moving earth in order to continue to cast material in a single direction. It can be appreciated that it would be a waste of labor and time to manually disconnect linkage between the tractors and the blade in order to side cast material to the same side.
In the case of using tractors in tandem, with one tractor situated behind the other and coupled thereto through a pivotable coupling, it is recognized that the tractive base of assembly is as narrow as a single tractor and there is little gain in stability with respect to lateral forces. Hence, when a wide bulldozer blade is connected to the tandem tractors high off-center forces tend to pivot one tractor about the other. Furthermore, the lead tractor provides the sole support and manipulative function of the blade with attendant complications such as having undesirable moment arms, for example.